Cis-olefins are an important source of pharmacological and biological compounds such as pheromones. Unfortunately, the synthesis of cis-olefins is a very difficult and expensive process because of the tendency of the reaction products to isomerize into inactive or inhibitory trans-isomers. An example of a simple cis-olefin which has proven difficult to produce economically is cis-9-tricosene, a housefly pheromone.
Many of the more classical syntheses require the use of alkynes or Wittig reagents to obtain the desired cis-stereochemistry. Although these reagents produce cis-olefins in high purity, their use in large scale production of pure cis-olefins is prohibitively expensive. Many cis-olefins, however, could be economically produced in high yields via a synthesis process which uses sulfonate esters, if a method could be developed to avoid isomerization from cis- to trans-isomers during the purification of the cis-olefin product. For instance, we have discovered that cis-9-tricosene (and many other cis-olefins) can be synthesized by a simple three step process beginning with readily available cis-alcohols. The first step of this process is to deprotonate the cis-olefinic alcohol to form a lithium or sodium alkoxide salt followed by reacting the olefinic alkoxide salt to form a sulfonate ester, then alkylating the sulfonate ester with an appropriate alkylmagnesium compound and a cuprous salt. After alkylation it is usually desirable to recover the cis-olefin in a highly purified form. Most schemes for purification of the cis-olefin rely on a distillation process. Unfortunately the cis-olefin is substantially converted to a trans-olefin during distillation from the alkylating reaction mixture containing the sulfonate ester.
It would also be advantageous if a process for the purification of cis-olefins formed by alkylating a sulfonate ester could be developed which is economical, simple, and easy to scale-up.
It is an object of this invention to provide an economical process for the purification of cis-olefins produced by alkylating a sulfonate ester.
It is also an object of this invention to provide a simple, easy to scale-up process for the purification of cis-olefins formed by alkylating a sulfonate ester.
It is a further object of this invention to provide a process for the purification of cis-9-tricosene, which is produced by alkylating a sulfonate ester.
Other aspects, objects, and several advantages of this invention will be apparent from the specification, including the examples and accompanying claims.